Preheat the oven to 350°F. Spray your loaf pans with floured cooking spray and set aside.
In a large microwave-safe bowl, melt the butter for about 1 minute on high power.
Add the canola oil, eggs, buttermilk, granulated sugar, light brown sugar, vanilla extract, ground cinnamon, ground cloves, allspice, and ground nutmeg. Whisk until combined.
Add the all-purpose flour, baking soda, baking powder, and a pinch of salt. Stir until just incorporated.
Fold in the grated carrots and optional raisins and nuts.
Pour the batter evenly into the prepared pans, filling them no more than halfway.
Bake in the preheated oven for 40 to 50 minutes until golden and a toothpick comes out clean.
Cool the cakes in the pans for 10 minutes before transferring to a wire rack.
In a stand mixer, combine cream cheese and butter, beating until smooth.
Gradually add confectioners’ sugar and vanilla extract. Beat until light and fluffy.
Frost the cooled loaves generously and slice to serve!